The disclosure generally relates to a semiconductor device with field plate and floating, complementarily-doped area and to a method for producing it. The semiconductor device includes a semiconductor body including a first electrode which is electrically connected to a first near-surface zone of the semiconductor body and of a second electrode which is electrically connected to a second zone of the semiconductor body. Between the first and the second electrode, a drift section is arranged in the semiconductor body. In the drift section, field plates with floating areas doped complementarily to the drift section are arranged which influence the field distribution in the drift section.
Such semiconductor devices have the characteristic that during a switching process, in which the device changes from a non-conducting into a conducting state, p-type charge carriers, that is to say holes, cannot flow quickly enough to these floating areas doped complementarily to the drift section, so that the field plates coupled on are capacitively drawn to a negative potential during the switching-on. This negative potential produces a depletion of charge in the drift section and can distinctly reduce the current flow on reactivation, that is to say after a transition from the non-conducting into the conducting state, until the potential of the field plates is raised again by leakage currents.
If an additional p−-conducting layer is implanted close to the surface for the floating p-conducting areas and possibly diffused out with a net doping approximately of the magnitude of the breakdown charge of the semiconductor which is approx. 2×1012 cm−2 with low-doped silicon, the floating areas doped complementarily to the n-conducting drift section can be discharged more rapidly. For this purpose, the p−-conducting layer of a MOSFET or of an IGBT is connected to a source potential or to an emitter potential, for example by overlapping with a body zone. However, the dopant boundary, and thus the conductivity of the discharge structure, is disadvantageously bound to the breakdown charge. Although p-type regions doped less are possible, they do not allow an optimum hole conductivity. In addition, the blocking capability is reduced since, in the non-conducting case, an additional vertical electrical field is produced at the p−-n−junction between p-conducting region of a body zone and an n-conducting drift section, which field is superimposed on the lateral field, but the blocking capability is reduced in this semiconductor device. This reduction in blocking capability can be verified by a compression of the equipotential lines at the upper pn junction. More highly doped p-type regions prevent a useful blocking capability.
It is also possible to discharge the floating areas doped complementarily to the drift section using p-channel MOSFETs to be provided additionally. Initially, the field plates and the floating areas doped complementarily to the drift section connected to the field plates become charged to a negative potential relative to a source or emitter electrode, respectively, as described, when the semiconductor device is switched on. If gate electrodes of the p-channel MOSFETs, to be provided additionally, which are connected to the floating areas doped complementarily to the drift section, are in each case placed at a negative potential, a p-conducting channel which enables the floating areas to become discharged is automatically produced when the semiconductor device is switched on. However, the field plates cannot be completely discharged via the additional p-channel transistors because of the finite starting voltage of these additional p-channel transistors.